Taxonomy & naming
Haplochromis melanopterus was described by the British ichthyologist Ethelwynn Trewavas in 1928, in her paper "Descriptions of five new cichlid fishes of the genus Haplochromis from Lake Victoria" (Annals and Magazine of Natural History, series 10). The type material came from the Tanzanian (then Tanganyika Territory) portion of the lake, in the Smith Sound area of the Mwanza Gulf. The name has stood in its original combination ever since; FishBase, the Catalog of Fishes and the CLOFFA checklist all carry it as Haplochromis melanopterus Trewavas, 1928.
The species belongs to the vast Lake Victoria haplochromine species flock, several hundred closely related cichlids that radiated explosively within the lake. Within that flock it is a paedophage, and on the strength of its feeding specialisation and a distensible, protractile mouth it has long been placed in the subgenus (or genus, depending on the author) Lipochromis — a group Greenwood erected for the lake's egg- and larvae-eating haplochromines. The atlas keeps the conservative Haplochromis heading because the boundaries of these segregate genera (Lipochromis, Astatotilapia, Mbipia and others) remain contested and most workers still file the whole assemblage under Haplochromis sensu lato; where it matters, the prose flags the Lipochromis placement. It is sometimes seen in the hobby and aquarist literature simply as "Lipochromis melanopterus."
Morphology
This is a modest, deep-bodied haplochromine. The largest recorded specimen measured about 5 in in standard length, so a mature fish is a hand-sized cichlid rather than a giant. The body is laterally compressed in the typical Victorian mould, and the species takes its name — melanopterus, "black-finned" — from its conspicuously blackish fins: the vertical fins (dorsal, anal and caudal) and the pelvic fins are dark, a feature Trewavas singled out in the original description. As in most haplochromines, breeding males are the colourful sex, while females and non-breeding fish are a plainer silvery-brown; the aquarium-trade fish photographed for the Cichlid Room Companion shows a darkly finned male. The functional hallmark of the Lipochromis paedophages, including this species, is the mouth: thick-lipped, widely distensible and protractile, with small teeth set deep in the oral mucosa rather than forming the firm scraping or crushing dentition of the algae- and snail-eating haplochromines. That loosely-toothed, expandable mouth is the apparatus that lets the fish engulf clutches of eggs and larvae whole.
Habitat
Haplochromis melanopterus is endemic to Lake Victoria and, as currently understood, restricted to the lake's Tanzanian (southern) waters, with its records concentrated in the Mwanza Gulf and Smith Sound. The holotype was collected over a mud bottom, and the species is treated by FishBase as a freshwater, benthopelagic fish of the inshore sublittoral. Most museum material was gathered between the mid-1970s and mid-1980s, in the years just before the lake's ecological collapse, largely from the northern Mwanza Gulf.
Lake Victoria itself is a shallow, equatorial, slightly alkaline lake. Surface temperatures across the lake typically run in the mid-20s Celsius (roughly 73–81 °F), and the open water is warm and well-lit year round, with a season of deep mixing around June–July when the thermocline breaks down. Recorded surface pH is on the alkaline side of neutral — commonly around 7.5 to 9 — and the water is soft to moderately mineralised. No in-situ chemistry has been published specifically for this species' microhabitat beyond the "mud bottom" note, so the figures here describe the lake it lives in rather than a measured envelope around the fish; the article is honest that the fine detail is thin.
Feeding
Haplochromis melanopterus is a paedophage — a specialist eater of other cichlids' eggs and young. The single point that anchors this is stark and first-hand: when the examined specimen's stomach was opened, it was packed with the early embryos of a cichlid fish. FishBase assigns it a trophic level of about 4.0, the level of a predator, consistent with a diet of developing fish rather than algae or detritus.
The Lake Victoria paedophages fall into two functional camps. "Snout-engulfers" thrust the snout into the mouth of a brooding female and suck out her clutch; egg- and larvae-eaters take spawned eggs and free embryos more opportunistically. With its widely distensible, protractile, small-toothed mouth, melanopterus is built as a snout-engulfer, raiding the buccal cavities of mouthbrooding females and drawing out their eggs and larvae — turning the flock's universal habit of oral brooding into a reliable food supply. It is, in effect, a brood parasite that eats rather than fosters. This is a low-vulnerability, narrowly specialised role in the community, and it depends entirely on a dense population of other breeding haplochromines to rob.
Mating
No detailed courtship account has been published for Haplochromis melanopterus specifically, so its mating behaviour must be read from the flock it belongs to. Lake Victoria haplochromines are polygynous maternal mouthbrooders with no lasting pair bond. Males develop bright nuptial colour and a pattern of egg-spots or finnage that functions in display, take up a small temporary territory or display site, and court passing females with lateral displays and quivering; a receptive female spawns with a male and then takes sole charge of the brood. Males contribute nothing after fertilisation. Given this species' paedophagous habit, the same buccal-brooding females that are courted and that carry broods elsewhere in the flock are also its prey — a fish of this kind lives among, and reproduces alongside, the very mouthbrooders it robs. Sexual dimorphism follows the haplochromine norm: colourful, displaying males and plainer, brood-carrying females.
Breeding
Like every member of the Lake Victoria species flock, Haplochromis melanopterus is a maternal (female) mouthbrooder. After spawning, the female collects the fertilised eggs into her mouth and incubates them there through hatching and the early free-swimming stage, releasing the developed fry and, for a time, taking them back in when threatened. No clutch count has been published for this particular species; Victorian haplochromines of its size typically carry small broods of a few dozen relatively large eggs — on the order of 20–80 — reflecting the trade-off mouthbrooders make between egg number and the safety of oral incubation. Parental care is entirely by the mouthbrooding female, brief by the standards of substrate-guarding cichlids and ending once the fry are free-swimming and foraging independently. The figures here are flagged as genus-typical for the flock rather than measured for melanopterus, which has not been studied as a breeder in any detail.
In the aquarium
Haplochromis melanopterus is rarely kept. It has no commercial fishery and no real presence in the general aquarium trade; the fish that do circulate are specialist captures and aquarist-bred lines of Lake Victoria haplochromines, traded under the "Lipochromis melanopterus" label among hobbyists who keep Victorian cichlids deliberately. There is no large body of husbandry experience to draw on, and most of what can be said is inferred from keeping related Victorian haplochromines.
A keeper who did acquire it would treat it as a typical inshore Victorian: a tank of moderate size for a roughly 4.5–5 in fish, hard, alkaline water in the lake's range (pH on the alkaline side of neutral, temperature in the mid-20s Celsius), strong filtration and good oxygenation, and the usual polygynous-mouthbrooder social structure of one male to several females to spread his attention. Tankmates should be other robust Victorian or rift-lake haplochromines of similar temperament; the species should never be hybridised with related Haplochromis, a real risk in mixed Victorian tanks. The honest complication is its diet. As a paedophage it is adapted to eating eggs and larvae, and in a community it can and does steal fry from brooding females — including, anecdotally, in captivity — so it is a poor neighbour for any fish you hope to breed. The fundamentals are not difficult; the fish is simply uncommon, ethically and practically a project for the dedicated Victorian-cichlid keeper, and best regarded as a conservation- and interest-driven aquarium fish rather than a trade staple.
Conservation
The IUCN Red List assesses Haplochromis melanopterus as Vulnerable under criterion D2 (assessed 31 March 2010 by Witte, de Zeeuw and Brooks), a category reflecting a very restricted range that could be pushed to a worse status by a single event. It is listed from Tanzania only, and its population trend is recorded as unknown. The threats named are the two that have reshaped Lake Victoria's fish fauna: the introduced Nile perch (Lates niloticus) and pollution from agricultural and forestry runoff. It carries no CITES or CMS listing.
The wider context is one of the most-studied ecological catastrophes in freshwater fish. From the 1980s the boom of the introduced Nile perch, compounded by eutrophication, declining water clarity and intense fishing, drove the collapse of the Lake Victoria haplochromine flock; a large fraction of its several hundred endemic cichlid species declined sharply or disappeared, and many are known only from museum collections made before the crash. Haplochromis melanopterus — a narrow-range paedophage whose food supply is the very flock that collapsed — sits squarely in the group hit hardest. The fact that most of its specimens were collected before the mid-1980s, and that its current status is uncertain, is itself a measure of how little is known about how it has fared.